This invention relates to the field of chemical probes, specifically chemical probes using analyte/reagent reactions and light absorption characteristics to determine chemical concentrations.
The measurement of the concentration of a particular chemical in a fluid mixture is a task common to many industrial and commercial processes. Historically, measurement has required physical sampling of a portion of the fluid mixture (the analyte). A reagent is reacted with the analyte sample, and the resulting properties (e.g., color) of the reaction products indicates the concentration of the chemical of interest. Such procedures are well known to those skilled in the art. Many processes and environments, however, make physical sampling and remote chemical analysis problematic. Physical samples are very difficult to obtain from hazardous, radioactive, or borehole environments.
Instruments have been proposed for analysis near the analyte source. Examples include the instruments described in Bredeweg, U.S. Pat. No. 5,368,725, Manz, U.S. Pat. No. 5,250,263, Stevens, U.S. Pat. No. 4,837,161, and Larsen, U.S. Pat. No. 5,389,524. Unfortunately, these instruments suffer from numerous shortcomings that decrease their usefulness in many applications. They all require the direct flow of analyte through the instrument. Stevens measures the properties of an analyte stream after intentional contamination with a reagent, limiting its use to applications where reagent contamination of a relatively low analyte volume is acceptable. Larsen requires a discrete, physical volume sample of analyte, a difficult operation in many remote environments. Other instrument designs are incapable of remote reagent/analyte reaction or remote analysis of the reaction products. Many also have impaired accuracy because the analyte/reagent reaction does not occur in the same volume as the analysis of the reaction products.
Accordingly, there is a need for a compact instrument that can determine chemical concentrations without requiring physical sampling of the analyte, and that is suitable for remote operation.